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Thread: Appropriate galvo or rotary solenoid for shutter?

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    Default Appropriate galvo or rotary solenoid for shutter?

    I'd like to build a super-high-speed camera shutter using a galvo or rotary solenoid. It's not a highly complicated application - essentially, rotating a bit of balsa wood about 2" long ~45 degrees - but it needs to do it fast. Really fast. ~1/10,000th of a second fast.

    The only actuators I've found that can beat one microsecond for such a rotation are those used in laser system galvos. Can anyone suggest such a device for my application?

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    Some high speed cameras use a rotating prism.

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    Not really suitable for the application, sadly. It's as much about killing ambient light for flash use as anything else.

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    Quote Originally Posted by jrshaul View Post
    Not really suitable for the application, sadly. It's as much about killing ambient light for flash use as anything else.
    what if you used a retro-reflective optical lever to bounce the light from the flash in and out of place?
    suppose you're thinkin' about a plate o' shrimp. Suddenly someone'll say, like, plate, or shrimp, or plate o' shrimp out of the blue, no explanation. No point in lookin' for one, either. It's all part of a cosmic unconciousness.

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    Quote Originally Posted by swamidog View Post
    what if you used a retro-reflective optical lever to bounce the light from the flash in and out of place?

    I'm going to fess up that I don't even know what this is. I don't think it'll work either, though.

    FWIW, it looks like some of the galvos are rated for 30,000 movements per second, and you can get them in $100 ebay laser kits. Anyone know where I could get such a galvo, and whether it might actually work?

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    Nope...sorry mate ....IMHO it won't work! ....movement in question is a tiny rotational "step".
    Cheers

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    Quote Originally Posted by jrshaul View Post
    I'd like to build a super-high-speed camera shutter using a galvo or rotary solenoid. It's not a highly complicated application - essentially, rotating a bit of balsa wood about 2" long ~45 degrees - but it needs to do it fast. Really fast. ~1/10,000th of a second fast.

    The only actuators I've found that can beat one microsecond for such a rotation are those used in laser system galvos. Can anyone suggest such a device for my application?
    I think your confusing settling time specs for small angle jumps versus what a galvo can actually do.

    More like 33 uS times for VERY small angle steps with a 3 mm square mirror on the shaft. Actual bandwidths for a galvo for a small angle are ~ 2.5 KHz, falling off to ~250 Hz for large angles. That is not done with a 2" unbalanced load, way too much inertia. When the shaft size increases to handle larger loads like yours, that speed falls off rapidly, leading to a very slow movement.

    I'm on sabbatical from PL as I work on my Masters, a friend pointed me to this post. I'm the guy who does this sort of high speed stuff here, as I have worked for university researchers for two decades. There are maybe 4-6 others on the board that can help you with the math, and two of them only lurk..

    PM me with an email, and given this weeks schedule, I can probably address your problem later this weekend. Your balsa requires a fairly large galvo, and there are tradeoffs based on galvo torque, shaft size, load inertia, scanner amplifier settings etc.. I can certainly point you in the right direction.

    Is this a "one shot" movement or a repetitive task? If its a "one shot" movement, there are probably far better ways then a galvo.

    The longer and wider the balsa, the faster the inertia climbs.

    I can certainly point you in the right direction with whom to talk to. Send me a PM with your email, and I'll get to you when I have time. That may be a while, because right now I'm FIFO buffering, first in, first out with priorities.

    1/10,000 is a little fast (understatement of the year) for that big a load, and the amount a galvo rotates is limited. Basically you could look at the time as a inverse product of inertia and angle. If you have low load inertia and a small movement angle, then galvos are very fast. 45 degrees is a VERY< VERY > VERY large jump for a galvo, and would need a specialized waveform to command the galvo for optimum speed.

    I'd need to know a lot more about your two inch piece of balsa before I could even begin to comment. In fact I'm going to get you the equations and let you do the math.


    However, If you have a large inertia and a large angle, then galvos are not that much faster then ordinary rotary solenoids, maybe only faster by a factor of 10 to 20.

    As has been pointed out, we use techniques like optical levers using mirrors, relay lenses with the shutter at the focus of the lenses, moving pinholes, two opposing shutters delayed from each other, two moving masks (common in 35 mm film) things like that to work around Inertia limits when doing photography, My current personal record is 4,000 frames per second continuously streamed to hard disk, with 300 nS exposures generated by a pulsed laser. That is slow by today's standards, but fast for 5 years ago when I worked with that sort of system.

    I basically need to scan in a copy of a book chapter on calculating how a load interacts with a galvo for you. This book has never made it on-line.
    You can then make a decision on what you need from what you learn.I'm betting you end up with a different solution to your problem, which right now is undefined based on your post.

    Also Balsa might not serve you well, you may be into carbon fiber or metal ... Balsa will probably bend under that kind of torque.

    What your talking about is really in the realm of spinning prisms or mirrors, acousto-optic cells, Electro-optic cells, or dental drills modified to act as continuously spinning shutters using optical relay levers. Things like that, and most are not common knowledge outside of defense, nuclear, industrial photography, and academia. Some of these devices can be had for cheap, on Ebay, these days.
    Steve
    Last edited by mixedgas; 07-24-2015 at 05:49.
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